An Introduction to Air Brakes

Jump to:
1. What the System Does
2. How It Works – Step by Step
3. Key Components Involved
4. Common Misconceptions
5. Why This Matters

Anchor 1

The purpose of an air braking system is to provide enough braking effort to safely slow and stop large vehicles. Compared with cars and light vehicles, heavy vehicles require significantly greater braking force, which makes air braking systems more suitable than hydraulic systems.

In addition to providing braking force, the system is designed so that the brakes are applied by default when air pressure is not present, improving safety when the vehicle is parked or if air pressure is lost.

How it Works - Step by Step

Anchor 2

Air is generated and stored
An engine-driven air compressor supplies compressed air to the system. This air is stored in reservoirs until required.
The system is charged
The compressor and reservoirs together form the charging part of the circuit, ensuring a supply of pressurised air is available.
The driver selects brake control
The driver uses two main controls:-- -
- A foot pedal to operate the service brakes
- A hand-operated lever to control the secondary air system
Releasing the spring-applied brakes
When the hand control valve is moved to the off position, air pressure is sent to the actuator. This compresses a powerful internal spring, releasing the brakes.
Applying the service brakes
When the driver presses the foot control valve, air is sent to the actuator to apply the service brakes.
Releasing the service brakes
When the pedal is released, the service air is exhausted and the brakes are released.
Applying the park brake
When the hand control valve is applied, secondary air is exhausted from the actuator. The power spring then re-applies the brakes.

Key Components Involved

Anchor 3

Air compressor
Supplies compressed air to the system and is driven by the engine.
Air reservoirs
Store compressed air until it is required.
Foot Control Valve (FCV)
Allows the driver to apply and release the service brakes using the foot pedal.
Hand Control Valve (HCV)
Controls the secondary air used to release or apply the spring-applied brakes.
Actuators
Convert air pressure into mechanical movement to apply or release the brakes.
Power spring
Applies the brakes when no air pressure is present.

Common Misconceptions

Anchor 4

Air brakes are not always applying braking force
Air pressure is used to control braking, not continuously apply it.
The system does not rely on air to stop the vehicle in all cases
The power spring applies the brakes when air pressure is exhausted.
Foot and hand controls serve different purposes
The foot control valve operates the service brakes, while the hand control valve manages the secondary air and park brake function.

Why This Matters

Anchor 5

Understanding the basic operation of air braking systems helps explain why they are used on heavy vehicles and how they differ from hydraulic braking systems. It also clarifies how safety is maintained through spring-applied braking when air pressure is not available.

This system-level understanding provides a foundation for learning about additional air brake components and control strategies.

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